public class BigMouthBird : Bird
{
    public BigMouthBird()
    {
        base.BirdType = BirdType.BigMouth;
    }

    protected override void FlySkill()
    {
        var velocity = base.rigidbodyXD.velocity;
        velocity.x = -velocity.x;
        base.rigidbodyXD.velocity = velocity;
    }
}